The present invention relates generally to wireless RF time hopping code-division-multiple-access (CDMA) spread spectrum communications systems, and specifically to ultrafast systems, which use individual ultrashort pulses (monocycle) signals in the picosecond (10.sup.-12) to nanosecond (10.sup.-9) range. Such ultrashort pulsed (monocycle) signals can also be very wide in instantaneous bandwidth. Before transmission and after reception, the system functions as a digital communications system. The carrier for such wireless communications systems is neither a frequency, amplitude, phase nor polarization carrier, but is due to the precise timing arrangements in a sequence of individual pulses provided by the digital coding schemes.
Whereas most wireless RF communications systems in the art use frequency-domain receiver designs based on the heterodyne, or super heterodyne principle, the receiver of the present invention is a time-domain homodyne receiver. Whereas prior art uses coding, e.g., in direct sequencing or frequency hopping, to achieve spreading and despreading of the signal with resultant processor gain, the present invention uses an ultrashort pulse as an individual signal always spread over a very wide bandwidth, as well as coding which determines the timing of such individual pulses within a sequence. Information is carried in a transmission by the pulse position modulation technique, i.e., by precise micro-deviation from the pulse sequence timing set by the channel code.
Due to the use of orthogonal coding schemes and the use of ultrafast pulse sequence techniques, it is possible to provide extremely high data rate wireless point-to-point communications, as well as wide-area voice and data communications.
Accordingly, it is an object of the present invention to significantly increase the data rate of wireless RF communications by using orthogonal coding schemes in ultrafast time hopping CDMA communications both in point-to-point and broadcast mode.
It is a further object of the invention to provide a communications system which can coexist without interfering with, or causing interference to conventional RF transmissions or other ultrafast time hopping CDMA users.
It is a further object of the invention to provide a wireless communications system which can interface with digital, e.g., optical fiber, communications systems.
It is a further object of the invention to provide a communications system which is robust against environmental notched filtering of frequency components in the transmitted signal.
It is a further object of the invention to provide a communications system which has substantial range at modest power, is small in size, weight and is not costly to manufacture.